countercurrent regeneration

Basic principles of ion exchange and description of the technology have already been presented in the section ion exchange. It is already been demonstrated that :

• in conventional co-current regeneration processes, it is impossible to systematically exhaust the regenerant when it is brought into contact with ion exchanger layers in a state of decreasing saturation;
• in conventional co-current regeneration using UFD or Upcore processes, ionic contamination of the lower layers by a regenerant and/or by the water pushing the regenerant which would be charged with ions to be removed, does not provide the high standards of water increasingly required by the industry.

Countercurrent regeneration eliminates these major drawbacks, improving both quality of the treated water and the performance of regeneration, therefore lower the operating costs; countercurrent regeneration consists of percolating the regenerating solutions against the flow of the liquid being treated. Countercurrent regeneration takes place either in upflow or downflow, depending on the direction of the percolation flow used during the saturation phase.

In either cases, it is essential to avoid :

• uneven distribution of the regenerating solutions, which could cause «channelling», with consequence of inadequate contact between resin and regenerant;
• layer disturbance, which could reduce the saturation gradient (the higher the gradient, the better is the countercurrent regeneration).

It is therefore essential to maintain an ion exchange bed fully compacted during the injection of the solution and during its displacement by water.

The various “blocking” methods, designed to control resin bed expansion, can be grouped into three categories.